Method and apparatus for making tubes

ABSTRACT

In a method of making a tube a sheet metal blank. having opposite longitudinal flanks is placed in a die of a shaping tool. At least one of the longitudinal flanks of the sheet metal is provided with a contact projection suitable for resistance pressure welding. The blank is pressed into a U-shaped cavity of the cavity by a ram to shape the blank into a U-shaped configuration which is then shaped between an upper mold and a lower mold of a molding press into a tubular profile with the longitudinal flanks confronting one another. The upper mold has in an area of the confronting longitudinal flanks oppositely poled electrode strips which are insulated against one another. During subsequent welding operation, the contact projection on the one longitudinal flank is welded to the confronting longitudinal flank as a result of welding heat generated through introduction of an electric current via the electrode strips into the longitudinal flanks and a clamping pressure by which the upper and lower molds are held together.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the priority of German Patent Application, Serial No. 10 2005 006 579.1, filed Feb. 11, 2005, pursuant to 35 U.S.C. 119(a)-(d), the content of which is incorporated herein by reference.

This is one of two applications both filed on the same day. Both applications deal with related inventions. They are commonly owned and have the same inventive entity. Both applications are unique. Accordingly, the following U.S. patent application is hereby expressly incorporated by reference: “Method and Apparatus for Making Tubes”.

BACKGROUND OF THE INVENTION

The present invention relates, in general, to a method and apparatus for making tubes.

DD 276 043 A1 discloses a method and apparatus for making thin-walled tubes from sheet metal blanks by using indirect lap welding. The apparatus includes a molding press having a shaping tool which is comprised of a lower forming piece, which has a semicircular cavity to embrace the blank from outside, a cylindrical mandrel with incorporated copper rail, and two upper forming pieces. A drawback of this construction is its complexity of the overall apparatus.

It would therefore be desirable and advantageous to provide an improved method and apparatus for making a tube from a sheet metal blank to obviate prior art shortcomings and to operate more efficiently.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a method of making a tube includes the steps of placing in a shaping tool a sheet metal blank having opposite longitudinal flanks, providing at least one of the longitudinal flanks of the sheet metal with contact projections suitable for resistance pressure welding, pressing the blank into a U-shaped cavity of a lower mold of the shaping tool by a ram to shape the blank into a U-shaped configuration, shaping the U-shaped blank between an upper mold and the lower mold into a tubular profile with the longitudinal flanks confronting one another, wherein the upper mold has in an area of the confronting longitudinal flanks oppositely poled electrode strips which are insulated against one another, and welding the contact projections on the one longitudinal flank to the confronting longitudinal flank as a consequence of welding heat generated through introduction of electrical current by means of the electrode strips into the longitudinal flanks, and an applied clamping pressure that holds the upper and lower molds together.

The present invention resolves prior art problems by joining the longitudinal flanks together through resistance projection welding in the area of the contact projections. No lap welding is involved. As the longitudinal flanks are held together under the pressure, the sheet metal blank is able to lie against the shaping tool. No mandrel is necessary to force the areas to be welded against one another and no mandrel needs to be pulled out from the tube or vice versa. As a result, the manufacturing process is simplified and faster to implement for producing various types of pressure-resistant tubes or other tubes for various applications such as, e.g., as dashboard support, door impact support, or for use in the chassis region for axles. Applications other than those in the automobile industry are, of course, also conceivable in the event a load-carrying capability of the tubular profile is desired.

There are many ways of arranging the contact projections. For example, the contact projections may be provided on one or both longitudinal flanks. The contact projections of the longitudinal flanks may be disposed in offset relationship or in pairs. An arrangement of the contact projections in offset relationship in particular results in quasi intermeshing of the longitudinal flanks. The geometry of the projection determines also whether or not the tubes are tight.

Provision of further manufacturing steps are, of course, also conceivable, such as subsequent welding operations to partly or completely weld together the longitudinal flanks, in the event the strength of the connection should meet locally more stringent demands.

According to another aspect of the present invention, an apparatus for making a tube includes a shaping tool having an upper mold and a lower mold for shaping a U-shaped blank into a substantially tubular profile, with the upper mold having electrode strips which are disposed in an area of confronting longitudinal flanks of the tubular profile in parallel relationship to the longitudinal flanks, wherein the electrode strips are insulated against one another and include contact surfaces facing an outer circumference of the tubular profile for introduction of a welding current into the tubular profile.

According to another feature of the present invention, the contact surfaces of the electrode strips may have a contour which conforms to the outer circumference of the tubular profile. The contact surfaces of the electrode strips may hereby be part of a shaping contour of the upper mold. In this way, the outer circumference of the tubular profile is protected against burning, and the service life of the electrode strips is increased.

In general, it is also possible to provide a plurality of individual electrodes lined up in rows to define overall an electrode strip which is in contact with the tubular profile at individual contact zones but not along the entire length of the tubular profile. Electrodes made of copper typically have a smaller wear resistance than a shaping tool of steel. To prevent excess wear in the area of the electrode strips, the contact region of the electrode strip may be pierced by the at the outer circumference of the tubular profile at even distances by the upper mold that carries the electrode strips. In other words, the electrode strip may have a generally comb-shaped configuration, with the spine of the electrode comb joining together all spaced-apart electrode fingers. The electrode fingers are hereby in contact with the outer circumference of the tubular profile and may continuously adjust as wear increases.

According to another feature of the present invention, the electrode strips may be configured as mirror images in relation to a longitudinal center plane between the longitudinal flanks to be welded.

According to another feature of the present invention, an insulation layer may be disposed in a longitudinal center plane between the longitudinal flanks to be welded, for separating the electrode strips form one another.

BRIEF DESCRIPTION OF THE DRAWING

Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:

FIGS. 1 a to 1 d are schematic views of forming steps for shaping a sheet metal blank into a tubular configuration;

FIG. 2 is a schematic illustration, on an enlarged scale, of a detail of an upper mold in accordance with the present invention; and

FIGS. 3 a to 3 c are schematic illustrations of four embodiments of sheet metal blanks for use in a method according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Throughout all the Figures, same or corresponding elements are generally indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the drawings are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.

Turning now to the drawing, and in particular to FIG. 1 a, there is shown a schematic illustration of a molding press, generally designated by reference numeral 1, for shaping a sheet metal blank 2 in a first manufacturing step from a flat configuration to a U-shaped configuration. The molding press 1 includes a shaping tool having a ram 3 and a lower mold 5 which is formed with a U-shaped cavity 4. After placing the flat blank 2 on the lower mold 5, the ram 3 is lowered in the direction of the lower mold 5 to force the blank 2 into the cavity 4 and thereby shape the blank 2 to assume the U-shaped configuration. This shaping step is shown in FIG. 1 b.

A subsequent second manufacturing step transforms the U-shaped blank 2 to a tubular profile R, as shown in FIGS. 1 c and 1 d. The U-shaped blank 2 of FIG. 1 b is placed into a cavity of the lower mold 5, as shown in FIG. 1 c. Subsequently, an upper mold 6 is moved in a direction of arrow P towards the lower mold 5 to shape the blank 2 into a tubular profile R. This is shown in FIG. 1 d. During the shaping operation, the initially parallel legs of the U-shaped blank 2 are curved inwards so that their longitudinal edges 7, 8 confront one another in midsection of the upper mold 6.

Referring now to FIG. 2, there is shown a schematic illustration, on an enlarged scale, of a detail of an upper mold 6 in accordance with the present invention, depicting the contact region of the longitudinal flanks 7, 8 of the tubular profile R. The longitudinal flanks 7, 8 abut each other via incorporated contact projections 9 and are welded together, using projection welding by which the longitudinal flanks 7, 8 are joined while being held together under pressure applied by the upper mold 6. A welding current is hereby introduced via electrode strips 10, 11 into the longitudinal flanks 7, 8 and thus into the contact projections 9. The electrode strips 10, 11 are disposed in the upper mold 6 adjacent to the longitudinal flanks 7, 8 and configured as mirror images in relation to a longitudinal center plane MLE between the longitudinal flanks 7, 8 being welded together. Extending in the longitudinal center plane MLE is an insulating layer 12 by which the electrode strips 10, 11 are separated electrically from one another.

The electrode strips 10, 11 have contact surfaces 13 of a contour conforming to the outer circumference of the tubular profile R and forming part of the shaping contour of the upper mold 6.

The introduced welding current seeks its path to the other electrode strip via the contact projections 9 between the longitudinal flanks 7, 8. As a result, the longitudinal flanks 7, 8 are welded together in the area of the contact projections 9. Depending on a toothed configuration of the sheet metal blank, the tube that can be removed from the molding press 1 after disengaging the upper mold may or may not be pressure-tight.

FIG. 3 shows three possible embodiments of sheet metal blanks 2 a, 2 b, 2 c. The sheet metal blank 2 a, shown in FIG. 3 a, has contact projections 9 formed along each of the longitudinal flanks 7, 8 in opposite relationship. Only the contact projections 9 come into contact during manufacture of the tubular profile R. The sheet metal blank 2 b, shown in FIG. 3 b has contact projections 9 in offset relationship so that the shaping of the blank 2 b into a tubular profile R results in an intermeshing engagement. In this way, opposing contact projections 9 and longitudinal flanks 7, 8 are respectively joined. The sheet metal blank 2 c, shown in FIG. 3 c, has contact projections 9 only along one of the longitudinal flanks 7, 8 (here longitudinal flank 7).

It will be appreciated by persons skilled in the art that the geometry of the contact projections 9 as shown in FIGS. 3 a to 3 c has been randomly selected for illustrative purposes of different options for positioning of the contact projections 9. Of course, the configuration or geometry as well as the number of contact projections 9 can be selected in any suitable manner that is appropriate for the situation at hand. For example, the contact projections 9 may also be of different width or height, or may be arranged at even distances from one another or at varying distances from one another.

While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. 

1. A method of making a tube, comprising the steps of: placing in a shaping tool a sheet metal blank having opposite longitudinal flanks; providing at least one of the longitudinal flanks of the sheet metal with contact projections suitable for resistance pressure welding; pressing the blank into a U-shaped cavity of a lower mold of the shaping tool by a ram to shape the blank into a U-shaped configuration; shaping the U-shaped blank between an upper mold and the lower mold into a tubular profile with the longitudinal flanks confronting one another, wherein the upper mold has in an area of the confronting longitudinal flanks oppositely poled electrode strips which are insulated against one another; and welding the contact projections on the one longitudinal flank to the confronting longitudinal flank as a consequence of welding heat generated through introduction of electrical current by means of the electrode strips into the longitudinal flanks, and an applied clamping pressure that holds the upper and lower molds together.
 2. The method of claim 1, wherein both longitudinal flanks are formed with said contact projections.
 3. The method of claim 2, wherein the contact projections of the longitudinal flanks are disposed in offset relationship.
 4. The method of claim 2, wherein the contact projections of the longitudinal flanks oppose each other in pairs.
 5. Apparatus for making a tube, comprising a shaping tool having an upper mold and a lower mold for shaping a U-shaped blank into a substantially tubular profile, said upper mold having electrode strips which are disposed in an area of confronting longitudinal flanks of the tubular profile in parallel relationship to the longitudinal flanks, said electrode strips being insulated against one another and including contact surfaces facing an outer circumference of the tubular profile for introduction of a welding current into the tubular profile.
 6. The apparatus of claim 5, wherein the contact surfaces of the electrode strips have a contour which conforms to the outer circumference of the tubular profile.
 7. The apparatus of claim 5, wherein the contact surfaces of the electrode strips are part of a shaping contour of the upper mold.
 8. The apparatus of claim 5, wherein the electrode strips are configured as mirror images in relation to a longitudinal center plane between the longitudinal flanks to be welded.
 9. The apparatus of claim 5, further comprising an insulation layer, disposed in a longitudinal center plane between the longitudinal flanks to be welded, for separating the electrode strips form one another.
 10. The apparatus of claim 5, wherein the contact surfaces of the electrode strip are pieced at uniform distances at the outer circumference of the tubular profile by the upper mold which carries the electrode strips.
 11. The apparatus of claim 5, wherein each said electrode strip has a generally comb-shaped configuration, with a spine and plural spaced-apart electrode fingers extending from the spine. 